LexerInput

Hi,

I am studying a way to parse text data directly from memory (without using 
aditional temporary buffers). My questions are:
For C Flex:
What is the procedure to make sure that after using scan_buffer() as input 
method for Flex, the directly-scanned memory buffer remains intact (the 
content is restored)?
For Flex++:
Is there a way to addapt LexerInput() in such a way the scanning is done 
directly from the memory instead of reading into an additional buffer? If 
so, I have the same question regarding to the preservation of the buffer.
Any information or link to something would be helpful.

Thanks and best regards,
Mihai